class Graph:    def __init__(self):        self.V = []class Vertex:    def __init__(self, x):        self.key = x        self.color = 'white'        self.d = 10000        self.pi = None        self.adj = []class Solution:    def BFS(self, G, s):        for u in G.V:            if u != s:                u.color = 'white'                u.d = 10000                u.pi = None        s.color = 'gray'        s.d = 0        s.pi = None        Q = []        Q.append(s)        while Q != []:            u = Q.pop(0)            for v in u.adj:                if v.color == 'white':                    v.color = 'gray'                    v.d = u.d + 1                    v.pi = u                    Q.append(v)            u.color = 'black'if __name__ == '__main__':    G = Graph()    r = Vertex('r')    s = Vertex('s')    t = Vertex('t')    u = Vertex('u')    v = Vertex('v')    w = Vertex('w')    x = Vertex('x')    y = Vertex('y')    r.adj = [s, v]    s.adj = [r, w]    t.adj = [u, w, x]    u.adj = [t, x, y]    v.adj = [r]    w.adj = [s, t, x]    x.adj = [t, u, w, y]    y.adj = [u, x]    G.V = [r, s, t, u, v, w, x, y]    m = Solution()    m.BFS(G, s)    for v in G.V:        if v != s:            print v.key, v.color, v.d, v.pi.key